It is known that residue from oil and gasoline spills at service stations, parking lots, and similar sites commonly remain at the site of the spill until washed away by water from rainfall or hose cleaning operation. The residue is often washed to a drain where it is likely to be carried to and mixed with the water supply from which drinkable water is ultimately taken. The protection of ground water and natural bodies of water requires systems for diverting or treating the water that contacts parking lots, roadways and other contaminated structures. Similar problems and environmental concerns arise at alternative sites generating waste water, and these various sources of contaminated water will generally be referred to as stormwater for the purposes of this application.
The stormwater may contain a variety of contaminants, including floating particulate such as plastics, or volatile fluids such as gas and oil residue that will tend to float on stationary water; non-floating particulate such as sand, silt and pebbles; and entrained contaminants such as fertilizer or other various organic or inorganic contaminants that may have leeched from upstream sites.
In order to effectively treat stormwater, it is often desirable to have multiple separation stages and, most typically, a preliminary mechanical separation phase that removes the heavier-than-water particulates and lighter-than-water contaminants, followed by a filtration phase which is designed to remove entrained contaminants or contaminants that could not be gravitationally separated.
In the prior art, a typical first stage separation apparatus would be the AquaSwirl Separator described in U.S. Pat. No. 6,524,473, or comparable products offered by Contech Stormwater Solutions, such as the Hydrodynamic Separation products, or the StormScreen or VortCapture screening products.
At the filtration stage, many products such as StormFilter and VortFilter products from Contech Stormwater Solutions, utilize cartridges which inherently restrict the maximum volume of water flow. Other filtration devices, such as the AquaFilter components described in U.S. Pat. No. 6,190,545, utilize horizontal filter beds and rely upon gravity to urge the water downward through filter media to effect treatment. Inherent in the use of gravitational urged or down flow filtration is some loss of head since the water level of the filtered stormwater is inherently lower than the unfiltered water by at least the height of the filter media. Furthermore, as the untreated stormwater is filtered downward through the filter media, particulates remain on the top surface of that filter media, tending to more rapidly clog the filtration media than would be necessary if particulate matter were removed.
It is desirable to utilize the horizontal filter configuration because of the greatly enhanced flow rates that can be maintained through such media in comparison to canister or other alternative arrangements.